void main() {
  Person p = Person();
  print(p);
  print(p is Object);
  Student s = new Student();
  print(s.tt);
}

class Person {
  String name;
  int age;
  int _tt;

  @override
  String toString() {
    return "111";
  }

  get tt {
    return _tt;
  }

  Person.withName(this.name);

  Person([this.name = "a"]) : this.age = 1 {
    print("person init");
  }

  void call() {
    print("$name->$age");
  }
}

class Student extends Person {
  void study() {
    print("study");
  }

  Student() : super('1') {
    print("student init");
  }
}
